A number of steam valves are provided in steam turbines of thermoelectric power plants, nuclear power plants, or the like in order to regulate the amount of steam according to changes in loads or to stop the supply of steam in abnormal cases. The steam valves are constituted of a main steam stop valve and a steam governing valve. The main steam stop valve is an ON/OFF valve that stops or releases the flow of steam. The main steam stop valve is a valve that closes, for example, when power generation is stopped and thereby stops steam from flowing into the steam turbine. The steam governing valve is a flow volume control valve that controls the flow volume of steam which flows into the steam turbine.
As steam valves of the related-art, a steam valve in which a main steam stop valve and a steam governing valve are housed in one valve case (valve body) is known, as described in PTL 1. This steam valve has a configuration in which the main steam stop valve and the steam governing valve are driven from the same direction on one axis. Pressure loss in the steam valve is directly connected to steam turbine efficiency, and having the least amount of pressure loss as possible is desired. Hence, this type of steam valve, which can lower the pressure loss without any obstacles, such as a valve shaft (valve rod), in a downstream fluid channel, has been widely used.